1. Field of the Invention
This invention relates to a thin film-forming method whereby a thin film having good qualities can be obtained by enhancing a wettability of a surface of a substrate through the pretreatment of the surface of the substrate before the thin film is formed on the surface of the substrate from a liquid, more particular a pre-treating method in such a thin film forming method.
2. Related Art Statement
A typical process to grow a thin film from a liquid is a plating method. In the plating treatment, for developing the quality of the thin film formed by the plating, for example, a surface of a substrate on which the thin film is formed is pre-treated through the cleaning the surface with a water, an acidic liquid or an alkaline liquid before the plating treatment. Moreover, in forming the thin film alongside a given pattern, a mask having an opening with a given pattern such as a resist frame is formed on the surface of the substrate on which the thin film is formed and thereafter, the surface of the substrate is pre-treated. Then, the thin film having a given pattern is formed in the opening of the mask.
The method is conventionally known as the pretreatment method, for example, that a substrate for a thin film to be formed is dipped into a pre-treating liquid or a pre-treating liquid is sprayed onto a surface of a substrate by a spray. For example, Kokai publication No. 1-119685 discloses the pre-treating process containing acidic liquid wash, acidic liquid wash rinse, mist spray and plating-after-rinse, successively, in a continuous plating line of steel ribbon. In this case, a dipping method is used for the acidic liquid wash, the acidic liquid wash rinse and the plating-after-rinse, and a method to spray water is used for the mist spray.
Although in a technical field requiring a high accuracy and a fine plating pattern such as an IC, an LSI and thin film magnetic head, a mask having an opening to define a plating pattern, the width of the opening in the mask become very small. For example, although a width of a magnetic pole of a writing thin film magnetic head is narrowed to about 1 xcexcm for enhancing a recording density, the width is tended to be much narrowed. Thus, in forming the magnetic pole by plating a magnetic material, the opening width of the frame to define the plating pattern is narrowed corresponding to the narrowing of the pole width. Even though the pole width is narrowed, the aspect ratio (the height of the opening/the width of the opening) is made large for maintaining the plating film thick to some degree.
Thus, in the conventional pre-treating method, the pre-treating liquid strides the opening due to its surface tension, etc., so that the liquid can not be sometimes stuck on a surface to be plated located on the bottom surface of the frame opening. Moreover, since the pre-treating liquid closes the frame opening, pores remain in the opening, resulting in the interiors of the pores being not plated.
The resist frame itself has a large aspect ratio due to the narrowing of the plating pattern. Thus, in spraying the pre-treating liquid with a spray, particularly, the resist frame suffers from a large dynamic damage, resulting in the destruction of the resist frame. Moreover, when the pre-treating liquid is exhausted to outside from the frame opening, the resist frame is damaged from its surface tension.
It is an object of the present invention to provide a pre-treating method suitable for forming a narrowed thin film pattern precisely.
It is another object of the present invention to provide a pre-treating method for forming a thin film which can minimize a damage to a resist frame.
It is still another object of the present invention to provide a pre-treating method suitable for automation.
Moreover, this invention relates to a method for forming a thin film, from a liquid, on a pre-treated surface of a substrate, and it is further object of the present invention to provide a thin film-forming method capable of forming a high quality thin film precisely.
A pre-treating method in a thin film-forming process according to the present invention comprising the steps of:
forming, on a surface of a substrate on which a thin film pattern is formed, a mask having a pattern to define a thin film-forming area having a pattern corresponding to the thin film pattern,
producing an atmosphere containing microparticles of a pre-treating liquid produced by micronizing a pre-treating liquid so as to have the diameters at least smaller than the minimum distance of the mask pattern, and
positioning the substrate into the atmosphere containing the microparticles of the pre-treating liquid and thereby sticking the microparticles on the thin film-forming.
In this invention, by positioning the substrate on which the thin film is formed in the atmosphere containing the floating microparticles of the pre-treating liquid and sticking the microparticles of the pre-treating liquid within the thin film-forming area on the substrate, the thin film-forming area has good wettability and good surface condition whereby it is easy for the material constituting the thin film to be deposited when the thin film is formed from the liquid. Consequently, the high quality thin film can be formed. The pre-treating liquid has the microparticles having the smaller diameters than the minimum distance of the mask pattern and the microparticles are stuck on the thin film-forming area. Thus, even though in a technical field requiring a precise and fine thin film pattern in an IC, an LSI, a thin film magnetic head and so on, the aspect ratio of the mask opening become large due to the narrowing of the thin film pattern, the microparticles of the pre-treating liquid can be stuck on the thin film-forming surface located in the bottom surface of the opening. Thus, unlike the conventional technique, the improper problem does not occur that the opening is closed by the sticking of the pre-treating liquid at the mask opening or pores remain in the opening. Consequently, a high quality thin film can be formed.
Furthermore, since the microparticles of the pre-treating liquid float freely in the atmosphere in which the substrate is positioned, unlike the conventional spray method, the pre-treating method according to the present invention can minimize the dynamic damage for the resist frame. Thus, even if a mask having a large aspect ratio opening is employed for narrowing the thin film pattern, the destruction of the mask can be avoided. Moreover, the mask does not suffer from the damage due to the surface tension generated by the exhaust of the pre-treating liquid to outside from between the frame.
In carrying out the pre-treating method according to the present invention, the atmosphere may be made of a pre-treating liquid containing gas molecules, aerified liquid microparticles, or both the gas molecules and the liquid microparticles.
In a preferred embodiment of the pre-treating method according to the present invention, the pre-treating liquid is composed of a water and the atmosphere contains its moisture vapor. Then, the water particles are adhered to gas molecules through their condensation. Since the moisture vapor is a gas containing water molecules, in thin case, the above microparticles of the pre-treating liquid means the water molecules. In this way, in using the moisture vapor as the microparticles of the pre-treating liquid, the temperature of the atmosphere containing the moisture vapor is preferably 200xc2x0 C. and over for protecting the heat damage. Moreover, when the temperature of the atmosphere containing the moisture vapor is 100xc2x0 C. and below, the relative humidity is preferably not less than 100%.
In another preferred embodiment of the pre-treating method according to the present invention, using water as the pre-treating liquid, the substrate is positioned in the atmosphere containing water microparticles obtained by aerifying the water as the pre-treating liquid and the aerified water microparticles are stuck on the surface of the substrate. In this case, the aerifying is preferably carried out by supersonic vibrating the water. Although at least the part of the atmosphere containing the water microparticles normally is composed of a moisture vapor, its amount is not much, different from the case of the pretreatment by moisture vapor.
In still another preferred embodiment of the pre-treating method according to the present invention, the pre-treating liquid is made of an acidic liquid or an alkaline liquid and the atmosphere contains the microparticles produced by aerifying the acidic liquid or the alkaline liquid. The acidic liquid or the alkaline liquid may be easily aerified by supersonic vibration. Moreover, the atmosphere may contain the microparticles as gas molecules from almost all acidic liquids or an alkaline liquid like ammonia. Furthermore, the atmosphere may contain gas molecules from an alcohol such as ethanol.
In the pre-treating method according to the present invention, some of the above water-treatment, the plating liquid-treatment, the acidic liquid-treatment and the alkaline liquid-treatment are appropriately used. For example, a mask having a pattern to define a thin film-forming area having a pattern corresponding to a thin film pattern is formed on a surface of a substrate for the thin film to be formed, and thereafter, the substrate is positioned in an atmosphere containing water microparticles to stick water microparticles on the substrate. Then, the substrate is positioned in an atmosphere containing microparticles of an acidic liquid or an alkaline liquid to stick the acidic liquid-microparticles or the alkaline liquid-microparticles on the substrate, and thereafter, water microparticles are also stick on the substrate to remove the acidic liquid-particles or the alkaline liquid-particles. Subsequently, alkaline liquid- or acidic liquid-microparticles are stuck on the substrate in an atmosphere containing the microparticles, and water microparticles are stuck on the substrate in an atmosphere containing the water microparticles to remove the alkaline liquid- or the acidic liquid-microparticles. After the last water-treatment, a plating liquid-treatment may be carried out.
In the case of positioning a substrate in an atmosphere containing both of microparticles of a pre-treating liquid and gas molecules produced by evaporizing a pre-treating liquid, the microparticles and the gas molecules may be made of the same pre-treating liquid or different pre-treating liquids. For example, the atmosphere may be made of moisture vapor microparticles and microparticles generated by aerifying an acidic liquid.
This invention relates to a method for forming a thin film having a given pattern on a surface of a substrate. In the forming method, the above pretreatment is performed on the substrate and thereafter, a thin film may be formed from a solution on the surface of the substrate in the condition that the substrate surface is wet by the pretreatment. In this case, for preventing the pre-treating liquid on the substrate surface from evaporating, water current may be flowed very weakly on the wet substrate surface by the pretreatment. Although the thin film can be made from the solution by various method, it may be preferably formed from a plating liquid. In this case, the plating may be carried out by electroplating or electroless plating.
As mentioned above, since the vaporization of the pre-treating liquid by heating and the aerification of the pre-treating liquid by an aerifying equipment utilizing supersonic vibration can control easily the diameters of the microparticles produced and the content of the microparticles in the atmosphere, the pre-treating method suitable for automation can be provided.